Long-lasting modifications of saccadic eye movements following adaptation induced in the double-step target paradigm

The adaptation of saccadic eye movements to environmental changes occurring throughout life is a good model of motor learning and motor memory. Numerous studies have analyzed the behavioral properties and neural substrate of oculomotor learning in short-term saccadic adaptation protocols, but to our knowledge, none have tested the persistence of the oculomotor memory. In the present study, the double-step target protocol was used in five human subjects to adaptively decrease the amplitude of reactive saccades triggered by a horizontally-stepping visual target. We tested the amplitude of visually guided saccades just before and at different times (up to 19 days) after the adaptation session. The results revealed that immediately after the adaptation session, saccade amplitude was significantly reduced by 22% on average. Although progressively recovering over days, this change in saccade gain was still statistically significant on days 1 and 5, with an average retention rate of 36% and 19%, respectively. On day 11, saccade amplitude no longer differed from the pre-adaptation value. Adaptation was more effective and more resistant to recovery for leftward saccades than for rightward ones. Lastly, modifications of saccade gain related to adaptation were accompanied by a decrease of both saccade duration and peak velocity. A control experiment indicated that all these findings were specifically related to the adaptation protocol, and further revealed that no change in the main sequence relationships could be specifically related to adaptation. We conclude that in humans, the modifications of saccade amplitude that quickly develop during a double-step target adaptation protocol can remain in memory for a much longer period of time, reflecting enduring plastic changes in the brain.     

Semantic similarity and immediate serial recall: Is there an effect on all trials

In immediate serial recall, items are better recalled when they are all drawn from the same semantic category. This is usually accounted for by a two-stage retrieval-based framework, in which, at recall, long-term knowledge is used to reconstruct degraded phonological traces. The category shared by list items would serve as an additional retrieval cue restricting the number of recall candidates. Usually, the long-term search set is not defined, but some authors have suggested an extended search set and others a restricted set that is composed of the most recently presented items. This was tested in an experiment in which participants undertook an immediate serial recall task either alone or under articulatory suppression with either semantically similar or dissimilar lists. A trial-by-trial analysis revealed that, in both quiet and suppression conditions, items from similar lists were better recalled on all the trials, including the first one. In addition, there was no interaction between semantic similarity and trial, indicating that the effect of similarity was of similar size on all the trials. The results are best interpreted within a proposal suggesting an extended long-term search set.     

Centering on figurative features during the comprehension of sentences describing scenes

Summary Subjects were asked to read sentences which described scenes containing objects. In the scene described in each sentence, a specific part of a particular object was necessarily implied as having an important role. The object was named but none of its parts were. The assumption was that the subjects, while processing the sentence and immediately afterward, would cognitively center on the important part, as a function of the context created by the sentence. Immediately after reading the sentence, the subjects were probed with a picture of either the important part, or of an unimportant part of the object. Judgments of the compatibility of this picture probe with the sentence were faster for pictures of important parts than for pictures of other parts. This was taken as supporting the hypothesis of cognitive centration. In a second experiment, in which words were used as probes instead of pictures, a purely verbal process to account for the results was ruled out. In a third experiment, subjects were given instructions to intentionally form visual images of the scenes described by the sentences. In this case, overall response times to the picture probes were shorter than in the absence of such instructions, but this decrease was greater for pictures of unimportant parts. This finding was interpreted as showing that imagery instructions increase the rate of activation of features to varying degrees as a function of the previous level of activation.     

Paired associate learning of action verbs with visual-or motor-imaginal encoding instructions

Summary It is suggested that visual-imaginal encoding of actions, i.e., imagining seeing somebody else performing a described action, should be distinguished from motor-imaginal encoding, i.e., imagining how one performs the action oneself. While both kinds of encoding should provide good item-specific information, only visual-imaginal encoding should also lead to good relational encoding of word pairs. In three experiments in which subjects had to learn verb pairs, we obtained supporting data for this assumption. Although CR performance was equal to FR performance under visual-imaginal encoding, under motorimaginal encoding CR performance was worse than FR performance. In principle, this finding parallels results obtained with imagined noun pairs and with performed verb pairs.The research reported here was supported by a grant from the Deutsche Forschungsgemeinschaft to J. Engelkamp and Hubert D. Zimmer. The paper was prepared during a stay of these authors at the Centre d'Études de Psychologie Cognitive, enabled by a grant of PROCOPE 311 pro     

Effects of linear and angular velocity on 2-, 4-, and 6-month-olds'' visual pursuit behaviors

We report on a study with 12 infants at each of 2, 4, and 6 months of age which examines the effects on infant visual pursuit of varying the target linear velocity (m/s) and the target angular velocity (deg/s) independently. Tracking performance is described in terms of five behaviors which characterize infant performance as a tracking trial unfolds: time to initial capture, duration of initial tracking, duration of initial break in tracking, frequency of interruptions in tracking, and mean duration of all tracking intervals. Interruptions in tracking become more frequent as linear velocity increases but less frequent as angular velocity increases. The mean duration of later tracking intervals is diminished relative to the duration of earlier tracking intervals in 4- and 6-month-olds, but not in the 2-month-olds. Differences in angular velocity may account for the conflicting reports of disruptions in object permanence studies relying on a visual tracking paradigm.     

Champ et effets de la négation argumentative: contre-argumentation et mise en cause

An argument can be taken as an operation of justification or as the product of this operation. But what about a counter-argument? This article is based on the hypothesis that there exists an operation of argumentative negation, which is both the argumentative and the negative equivalent of the operation of justification. Justification and argumentative negation necessarily act on assertions, for they are active at the level of the epistemic modalities of statements. As an operation, a counter-argument can thus be described, as the application of an argumentative negation; as a product, it can be described as an argument the conclusion of which shows traces of negative modality. Two uses of argumentative negation are distinguished here: counter-argumentation and calling into question. The former can lead only to assertive conclusive statements, but the latter can also lead to directives or commissives. This leads the authors to introduce the notion of pseudo-argument, besides those of argument and counter-argument. It is shown in particular that when a pseudo-argument is rejected, argumentative negation has the effect of making evident an underlying argument. With respect to the latterit functions as a counter-argumentation, whereas with respect to the illocutionary act accomplished by the conclusive statement, it functions as a calling into question of a condition of satisfaction for this act. This article also defines certain characteristics of argument, proposes criteria for identifying argumentative negation in polemical conversations, and distinguishes four modes of counter-argumentation.     

Siblings of children with mental retardation: Family characteristics and adjustment

Siblings of children with mental retardation may be at greater risk for adjustment problems because of family stress related to the needs of the child with mental retardation. Family dimensions were investigated to determine their relationship to sibling adjustment. Adjustment of 12 siblings of children with mental retardation was examined in relationship to family dimensions. These relationships were compared to those for children from families without a disabled child. For both groups, self concept was positively associated with family cohesion, and social competence was positively associated with family promotion of independence. For only the siblings of the mentally retarded children, family conflict was inversely related to social competence, and family organization was positively related to sibling self concept. Our results suggest that family conflict and disorganization appear to have a more negative effect in families with a child with mental retardation.